A study commissioned by the China Emission Accounts and Datasets (CEADs) group in association with the University of East Anglia has claimed that cement structures are a substantial — but overlooked — absorber of carbon emission. The study indicates that existing cement stocks absorb around 1 billion tons of atmospheric CO2 each year on an annual basis. The mortar, concrete, and rubble from demolished buildings can gradually absorb CO2 through a process called carbonation. As CO2 from the atmosphere enters tiny pores in the cement, it comes in contact with a variety of chemicals and water trapped there. The ensuing reactions convert the CO2 into other chemicals. It is estimated that 4.5 gigatons of carbon (GtC) has been reabsorbed in carbonating cement material from 1930 to 2013. A gigaton is a unit of explosive power equivalent to 1 billion tons of TNT. This reabsorption in carbonating cement material from 1930 to 2013 might have offset 43 per cent of the CO2 emissions from production of cement over the same period. The findings were published in the journal Nature Geoscience. The researchers focused on four raw materials — concrete, mortar, construction cement waste and cement kiln dust.